Checking rear thrust angle
Thread Starter
Safety Car
Joined: Nov 2003
Posts: 4,969
Likes: 2
From: Lake Worth FL
St. Jude Donor '03-'05-'06 & '12
Checking rear thrust angle
Is my method valid for checking rear thrust angle? I tied a string between two jackstands that run the length of the car. Placed them so that the line is just touching the rear rim (both front and rear edges), then measure the distance from the string to the front spindle. If the number matches on both sides, thrust angle should be set, correct? Then from there I will set the rear toe. Sound good?
Le Mans Master
Joined: Feb 2000
Posts: 5,708
Likes: 1
From: Bedford NH
Cruise-In II Veteran
Here's what I do:
I use a laser and put it against the (in this case) rear wheel and shine it to a point on the ground adjacent to the front wheel centerline. Do this for each side and the distance should be the same on each side, regardless of whatever toe setting you want. If it is not, adjust the ties rods accordingly. As far as accuracy goes, .25 inch at 100 inches is only .143 degrees so if you are within the laser beamwidth, it is "dead-nuts".
I use a laser and put it against the (in this case) rear wheel and shine it to a point on the ground adjacent to the front wheel centerline. Do this for each side and the distance should be the same on each side, regardless of whatever toe setting you want. If it is not, adjust the ties rods accordingly. As far as accuracy goes, .25 inch at 100 inches is only .143 degrees so if you are within the laser beamwidth, it is "dead-nuts".
Melting Slicks
Joined: Dec 2003
Posts: 3,141
Likes: 0
From: Charlotte NC
I assume you can do a similar method for the fronts? I was thinking about the dave farmer method (or any home method), and what keeps you from measuring toe inccorectly...yes, your overall toe can be measured, but who says that one wheel is not more or less in one direction?? Yes, you can tell by how your steering wheel is when driving, but that would cuase alot of guessing and trial and error
Le Mans Master
Joined: Feb 2000
Posts: 5,708
Likes: 1
From: Bedford NH
Cruise-In II Veteran
Yes, turn the steering wheel dead straight and do it towards the rear. I actually do it when the entire car is supported on jackstands that are on the a-arms so the suspension is loaded. Then I drop a plumb bob line down from the spindle end to the floor and make a mark on the floor. Put in a few lug nuts to hold the rotor on, then use the laser on the rotor face and shoot it to the plumb bob mark. Since it is up on jack stands, it is super easy to adjust the tie rods. Again, the distance from the laser to the mark on the floor is not important, but they need to be the same left to right. The cool thing is if you choose to run asymetrical camber ( I.e. Lime Rock Park) a few mm's does not matter much it will track straight within a tenth of a degree or so.
Gary Hoffman
Hardbar.net
Gary Hoffman
Hardbar.net
Premium Supporting Vendor
Joined: Aug 2001
Posts: 5,364
Likes: 38
From: King George VA
I use a method not quite as accurate as Gary's, but easier and probably accurate enough.
I have a set of toe plates which cost about $65 and can measure toe to within 1/32". Easy to get total toe with them, but impossible to get each side's toe.
To get the thrust angle, I use the lazy man's method of what Gary describes above: I put a six foot aluminum level bar against the side of each rear tire and look down the inside edge of the level like a gunsight. It is very obvious if there is a difference between the two sides of the car.
Not sure why you would want to do that. I measure toe and thrust angle with the car on a perfectly level surface. If I have to adjust toe, I adjust it, then put it back on the level surface. In practice, toe isn't that sensitive to a level surface, but camber and caster are.
I have a set of toe plates which cost about $65 and can measure toe to within 1/32". Easy to get total toe with them, but impossible to get each side's toe.
To get the thrust angle, I use the lazy man's method of what Gary describes above: I put a six foot aluminum level bar against the side of each rear tire and look down the inside edge of the level like a gunsight. It is very obvious if there is a difference between the two sides of the car.
cool...the next question is, how do you safely put the car on jack stands and load the suspension at the same time? any pictures on how to do that?
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Thread Starter
Safety Car
Joined: Nov 2003
Posts: 4,969
Likes: 2
From: Lake Worth FL
St. Jude Donor '03-'05-'06 & '12
Just had a thought...the rear cradle on my car turned out to be off left to right. When installing my camber plates, I had to make a pretty significant change to the passenger side to get it to match the drivers side. If I'm shooting for a matching measurement at the front spindle with a string or laser, I'd need to account for this offset, correct?
Edit: never mind, if the frame is correct where the upper arms are attached, the camber plate variance should eliminate the difference. Thus measurement should still be valid. I think.
Edit: never mind, if the frame is correct where the upper arms are attached, the camber plate variance should eliminate the difference. Thus measurement should still be valid. I think.
Last edited by dmtnt; Mar 23, 2005 at 09:37 PM.
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